Due to recent developments in electronics and communication technologies, researches on wearable devices are expanding. It is expected that cloth, various life or cultural products including clothes, and accessary based on inter-object communication will be informatized. Such an informatization technology requires a technology related to an energy source for operating an electronic device mounted in such products. As a technique for securing the energy source, an energy harvesting technology for obtaining energy from vibration, photo-electricity, or heat is being spotlighted.
However, in order to actually implement a wearable device, it is still necessary to achieve technical improvements related to a secondary battery for storing energy generated by using the energy harvesting technique accompanied with development of such energy sources.
For example, for various electric and electronic devices or display devices applicable to fabric products, such as clothes and hats that are used for a long time in daily life by a user, techniques regarding a second battery for supplying power to those devices or storing power produced by the energy harvest devices are demanded. Furthermore, in order to easily utilize electric power stored in the secondary battery, it is necessary to secure user convenience for using the secondary battery together with wearable devices.